It worked great a few months ago, but when I went to do some further cutting today (very soft wood of a pinewood derby car), I noticed that it was very difficult to move the router along the wood (in the past it was actually hard to control, now it was hard to move).

I forced it along for a little bit, but then noticed a burning smell and could see the wood turning black.

Thanks. I haven't tried another one as I can't find the rest of the set, plus the others might be too big for the careful work I need to do. I'll see if I can find the others though and at least test it on some spare wood.

I agree it's the bit... but you also need to keep in mind that "trim routers" are just that... they are for very light trimming. You can't use them like a full size 2 or 3 hp router. They are good for trimming laminate and putting small roundovers on wood... not much more.

If you are trying to hog out a lot of wood with it, that is probably part of the problem.

I agree, most likely the bit. But a couple of other things to keep in mind. You need to keep your motion steady, as moving your router too slowly along the wood, lingering as I sometimes refer to it, can result in burning. Also, and this would more likely contribute to chipping and skipping than burning, although I think that it could be a factor, make sure that you are moving your router in the right direction along the piece. That's left to right when routing an edge directly in front of you, or right to left if you are shaping the edge away from you.

Thanks everybody. Something definitely changed since the last time I used it a month or so ago to today. It used to go through the derby car like butter (really soft wood) and was really hard to control. Today, even with decent pressure, it was very hard to move through the wood. I'll try to clean the bit and see if it's gunked up.

I don't use a router often enough to remember the direction so I always make a pass with a scrap piece of wood to tell me which direction I need to go. Of course when I was younger I had a better memory

If it helps you to remember it, just think of the old Norelco commercials... "lift, and cut". The router bit is only sharp when it is being pushed in the correct direction (left to right as aka pedro said) so it can "lift and cut". If you go the other way (right to left) it will cut but not as effectively... and might tend to burn if you try.